Chronic Beryllium Disease is caused by an immune response to inhaled beryllium, and occurs in 1 to 5% of the beryllium worker population. A critical feature of CBD is hypersensitivity to beryllium. Beryllium hypersensitivity is typically assayed in vitro using lymphocytes isolated from peripheral blood samples and thymidine incorporation. We have developed a flow cytometry assay for the analysis of blood lymphocyte proliferation in response to a challenge with soluble beryllium. The test has been validated using peripheral blood samples from patients diagnosed with Chronic Beryllium Disease. More recently, we have combined cell cycle analysis with immunophenotype in the same assay. In collaboration with Environmental Safety and Health Division, the Immuno-Flow Lymphocyte Proliferation Test is being applied to screen the LANL beryllium worker cohort and other berylliul worker cohorts in the DOE system for hypersensitivity to beryllium.